Page:Evolution of the thermometer.djvu/29

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his death, Fludd describes a "Speculum calendarium," which was a simple thermoscope of the usual pattern, and says he found it in a manuscript more than 500 years old. This certainly disposes of the pretensions of those who claim Fludd as an originator.

The instrument figured in Fludd's book represents the usual inverted air thermoscope in a basin of water, the stem being divided into fourteen degrees, of which seven are below and seven above a central line named "sphaera aequalitis," a curious forerunner of our modern zero with plus and minus degrees.

The list of those to whom the invention of the thermometer has been ascribed should include the Servite monk Fra Paolo Sarpi, named by Fulgenzio for the honor; "Father Paul," as he is called, does not seem to have used the instrument before 1617, and does not mention it in his writings.

Before the days of academies of science and of periodical literature, communication between European savants was maintained by personal visits and by correspondence. One of the most active intermediaries between scientists in the first half of the seventeenth century was a French theologian, Father Marin Mersenne;